Carbohydrates Classification and Examples
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Questions and Answers

What type of linkage is primarily found in amylose?

  • α-1,4 linkage (correct)
  • β-1,4 linkage
  • γ-1,4 linkage
  • α-1,6 linkage

Which polysaccharide serves as a storage form of glucose in animals?

  • Chitin
  • Starch
  • Cellulose
  • Glycogen (correct)

Which structural polysaccharide is primarily composed of β-(1-4) glycosidic linkages?

  • Inulin
  • Glycogen
  • Starch
  • Chitin (correct)

What is the primary use of cellulose in the human diet?

<p>Acts as a ruffage (A)</p> Signup and view all the answers

What elements primarily make up carbohydrates?

<p>Carbon, hydrogen, and oxygen (A)</p> Signup and view all the answers

Which feature distinguishes glycogen from starch?

<p>Branching frequency (C)</p> Signup and view all the answers

What is the primary function of glycosidic bonds in carbohydrates?

<p>To join monosaccharides (D)</p> Signup and view all the answers

What is the main building block of chitin?

<p>N-acetylglucosamine (A)</p> Signup and view all the answers

Where is cellulose most commonly found in nature?

<p>Plant cell walls (A)</p> Signup and view all the answers

What distinguishes an O-glycosidic bond from an N-glycosidic bond?

<p>The non-carbohydrate group attached (B)</p> Signup and view all the answers

Which of the following accurately describes inulin?

<p>A long chain of D-fructose with β-1,2 linkages (B)</p> Signup and view all the answers

What is the general formula for carbohydrates?

<p>Cx(H2O)y (D)</p> Signup and view all the answers

Which common carbohydrate is a disaccharide of physiological significance?

<p>Maltose (D)</p> Signup and view all the answers

What is the significance of pentoses in human metabolism?

<p>They are used to form genetic material (A)</p> Signup and view all the answers

Which of the following best describes glycoside formation?

<p>It occurs through the interaction of hydroxyl groups (C)</p> Signup and view all the answers

Which of the following carbohydrates is classified as a hexose?

<p>Fructose (D)</p> Signup and view all the answers

What is the main function of phosphorylating glycolytic intermediates?

<p>To lower their activation energy for enzymatic reactions (B)</p> Signup and view all the answers

Which of the following substances inhibits pyruvate kinase activity?

<p>Fatty acids (B)</p> Signup and view all the answers

In which situation is anaerobic glycolysis primarily utilized?

<p>During high-intensity exercise (C)</p> Signup and view all the answers

What role do cofactors like K+ and Mg2+ play in pyruvate kinase activity?

<p>They stabilize the active site of the enzyme (B)</p> Signup and view all the answers

Which pathway involves the conversion of pyruvate to lactate?

<p>Anaerobic glycolysis (A)</p> Signup and view all the answers

What is the role of aldose reductase in the metabolism of glucose?

<p>Forms sorbitol from glucose. (C)</p> Signup and view all the answers

Which enzyme is responsible for converting sorbitol to D-fructose in certain tissues?

<p>Sorbitol dehydrogenase (A)</p> Signup and view all the answers

What metabolic defect is caused by a deficiency in fructokinase?

<p>Essential fructosuria (D)</p> Signup and view all the answers

Which product is formed when lactose is hydrolyzed?

<p>Glucose and galactose (B)</p> Signup and view all the answers

What is the consequence of the absence of aldolase B in metabolism?

<p>Severe hypoglycemia and jaundice (D)</p> Signup and view all the answers

UDP-galactose is primarily used for which of the following?

<p>Formation of glycogen and glycoproteins (A)</p> Signup and view all the answers

Which condition results from a deficiency in galactokinase?

<p>Non-classical galactosemia (C)</p> Signup and view all the answers

What is a consequence of lactose intolerance?

<p>Deficiency of β-galactosidase (D)</p> Signup and view all the answers

What is the overall reaction when pyruvate is converted to Acetyl CoA?

<p>Pyruvate + NAD+ + CoASH → Acetyl CoA + NADH + H+ + CO2 (B)</p> Signup and view all the answers

Which factor increases the activity of pyruvate dehydrogenase (PDH) according to the regulatory mechanisms?

<p>Increased insulin levels (A)</p> Signup and view all the answers

Which enzyme is key in the oxidative decarboxylation of isocitrate?

<p>Isocitrate dehydrogenase (A)</p> Signup and view all the answers

What is produced along with NADH during the conversion of α-ketoglutarate to succinyl CoA?

<p>CO2 (A)</p> Signup and view all the answers

What role does citrate play in its own synthesis reaction?

<p>Inhibitor of citrate synthase (C)</p> Signup and view all the answers

Which of the following coenzymes is required by the pyruvate dehydrogenase complex?

<p>CoA (B)</p> Signup and view all the answers

What type of phosphorylation occurs during the cleavage of Succinyl CoA?

<p>Substrate-level phosphorylation (C)</p> Signup and view all the answers

How many ATPs are generated from the oxidation of malate to oxaloacetate?

<p>3 ATPs (D)</p> Signup and view all the answers

What is the primary role of hexokinase in glucose metabolism?

<p>Converts glucose to glucose 6-phosphate (A)</p> Signup and view all the answers

What distinguishes glucokinase from hexokinase?

<p>Glucokinase operates at high glucose levels. (C)</p> Signup and view all the answers

Which enzyme is responsible for the conversion of fructose 1,6-bisphosphate into triose phosphates?

<p>Aldolase (C)</p> Signup and view all the answers

What effect does ATP have on the enzyme phosphofructokinase I (PFK I)?

<p>Inhibits PFK I (A)</p> Signup and view all the answers

What is the main purpose of the reaction catalyzed by glyceraldehyde 3-phosphate dehydrogenase?

<p>To oxidize glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate (A)</p> Signup and view all the answers

What occurs during the conversion of 2-phosphoglycerate to phosphoenolpyruvate?

<p>Reversible reaction catalyzed by enolase (A)</p> Signup and view all the answers

Which molecule does phophoglycerate mutase act upon?

<p>3-phosphoglycerate (D)</p> Signup and view all the answers

What is the role of fluoride in the context of the glycolytic pathway?

<p>Inhibits enolase (D)</p> Signup and view all the answers

Flashcards

Carbohydrates Classification

Carbohydrates are classified based on their structure, primarily into simple and complex carbohydrates.

Carbohydrate Structure

Carbohydrates consist of carbon, hydrogen, and oxygen atoms, often represented by the general formula Cx(H2O)y.

Monosaccharides

The simplest form of carbohydrates, consisting of a single sugar unit.

Disaccharides

Carbohydrates formed by the combination of two monosaccharides.

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Glycosidic Bonds

Bonds that join monosaccharides together to form larger carbohydrates.

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O-Glycosidic Bond

A type of glycosidic bond where a hydroxyl group (-OH) on a non-carbohydrate molecule connects with a hydroxyl group on a monosaccharide.

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N-Glycosidic Bond

A type of glycosidic bond where an amine group (-NH2) on a non-carbohydrate molecule connects with a hydroxyl group on a monosaccharide.

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Glycoside Formation

When a hydroxyl group on one monosaccharide reacts with the hydroxyl group of another substance (carbohydrate or non-carbohydrate), forming a glycoside.

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Starch

Storage form of glucose in plants, a polymer of glucose units.

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Amylose

Unbranched chain of glucose units in starch, linked by α1→4 linkages.

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Amylopectin

Branched chain of glucose units in starch, 24-30 units apart, linked by α1→6 linkages.

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Glycogen

Storage form of glucose in animals, a highly branched polymer of glucose units.

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Cellulose

Important structural polysaccharide in plant cell walls, a linear glucose polymer with β-(1-4) linkages.

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Chitin

Structural polysaccharide found in exoskeletons and some fungal cell walls, consisting of N-acetylglucosamine units with β-1,4 linkages.

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Inulin

Long chain homoglycan of fructose with β-1,2 linkages, a reserve carbohydrate in tubers.

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Dietary Fiber

Indigestible component of plant cell walls, largely cellulose, important for gut health.

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Hexokinase vs Glucokinase

Both enzymes catalyze the conversion of glucose to glucose 6-phosphate (G6-P). Hexokinase is found in most tissues and works when blood glucose is low, while glucokinase is primarily in the liver and acts when blood glucose is high.

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Irreversible Step in Glycolysis

A step in glycolysis that cannot go backward spontaneously. Energy is used to make the reaction happen, preventing the reverse process.

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Phosphofructokinase (PFK I)

An enzyme that catalyzes the irreversible and regulatory phosphorylation of fructose 6-phosphate to fructose 1,6-bisphosphate. It's a major control point for glycolysis.

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Aldolase

The enzyme that cleaves fructose 1,6-bisphosphate into two triose phosphates: dihydroxyacetone phosphate (DHAP) and glyceraldehyde 3-phosphate (Gly3-P).

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Glyceraldehyde 3-Phosphate Dehydrogenase (GAPDH)

The enzyme that oxidizes glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate, producing the first high-energy compound in glycolysis.

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Substrate Level Phosphorylation (SLP)

The direct transfer of a phosphate group from a high-energy molecule to ADP, forming ATP. This occurs without the use of an electron transport chain.

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Enolase

The enzyme that dehydrates 2-phosphoglycerate to phosphoenolpyruvate (PEP), a high-energy compound in glycolysis.

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Fluoride Inhibition

Fluoride specifically inhibits the enzyme enolase, disrupting the glycolytic pathway.

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Pyruvate Dehydrogenase Complex

A multienzyme complex responsible for converting pyruvate into acetyl CoA, linking glycolysis to the TCA cycle.

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What is the main function of the Pyruvate Dehydrogenase Complex?

The Pyruvate Dehydrogenase Complex converts pyruvate to acetyl CoA, a key step in the link between glycolysis and the TCA cycle.

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TCA Cycle Input

Acetyl CoA, which is derived from pyruvate, is the primary input for the TCA Cycle.

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TCA Cycle Regulation

The TCA Cycle is carefully regulated by factors like ATP:ADP ratio, NADH:NAD+ ratio, and acetyl CoA availability. High ATP and NADH levels inhibit the cycle,

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Citrate Synthase

The enzyme that catalyzes the first step of the TCA Cycle, combining acetyl CoA with oxaloacetate to form citrate.

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Isocitrate Dehydrogenase

A key regulatory enzyme that catalyzes the oxidative decarboxylation of isocitrate to α-ketoglutarate in the TCA cycle.

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Succinyl CoA Synthetase

This enzyme catalyzes the cleavage of succinyl CoA to succinate during the TCA cycle, generating GTP through substrate-level phosphorylation.

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Fumarase

The enzyme that catalyzes the hydration of fumarate to malate in the TCA cycle.

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Sorbitol Pathway

A metabolic pathway involving the conversion of glucose to sorbitol, then to fructose, particularly important in certain tissues like lens, retina, and placenta.

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Galactose Metabolism

The process of breaking down galactose, a sugar found in milk, into glucose for energy production.

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Essential Fructosuria

A metabolic disorder caused by a deficiency in fructokinase, resulting in the inability to properly metabolize fructose.

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Hereditary Fructose Intolerance

A serious genetic condition where the body lacks the enzyme aldolase B, leading to an inability to break down fructose.

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Lactose Intolerance

The inability to digest lactose (milk sugar) due to a deficiency in the enzyme lactase.

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Non-classical Galactosemia

A less severe form of galactosemia caused by a deficiency in the enzyme galactokinase.

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Galactitol

An alcohol produced from the conversion of galactose by the enzyme aldose reductase.

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Pyruvate Kinase

An enzyme that catalyzes the irreversible transfer of a phosphate group from phosphoenolpyruvate (PEP) to ADP, forming ATP and pyruvate. This is a key step in glycolysis and an example of substrate-level phosphorylation (SLP).

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Pyruvate Kinase Activation

Pyruvate kinase is activated by factors that promote glycolysis, such as high levels of fructose 1,6-bisphosphate (F1,6-BP), high carbohydrate intake, and high insulin levels.

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Pyruvate Kinase Inhibition

Pyruvate kinase is inhibited by factors that signal high energy states and alternative fuel sources, such as increased levels of cAMP, alanine, fatty acids, and acetyl CoA.

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Phosphorylated Intermediates in Glycolysis

Phosphorylated molecules in glycolysis are trapped within the cell due to their negative charge and the impermeability of the plasma membrane. This keeps them from diffusing out of the cell. They also play a crucial role in energy conservation. High-energy intermediates like 1,3-bisphosphoglycerate (1,3-BPG) and PEP donate phosphate groups to ADP, forming ATP.

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Anaerobic Glycolysis

A metabolic pathway that occurs in the absence of oxygen, where pyruvate is converted to lactate by lactate dehydrogenase. This process regenerates NAD+ for glycolysis to continue even without oxygen.

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Study Notes

Carbohydrates

  • Carbohydrates are polyhydroxy aldehydes or ketones and their derivatives.
  • They consist of carbon (C), hydrogen (H), and oxygen (O) atoms.
  • They are represented by the general formula Cx(H2O)y.
  • "Saccharide" comes from Greek, Sanskrit, and Latin words for table sugar.

Classification of Carbohydrates

  • Monosaccharides: Classified based on the number of carbon atoms (trioses, tetroses, pentoses, hexoses, heptoses). Further classified as aldoses or ketoses based on functional groups.
  • Oligosaccharides: Contain 2 to 10 monosaccharide units.
    • Disaccharides (two monosaccharides)
    • Trisaccharides (three monosaccharides)
    • Etc.
  • Polysaccharides: Composed of many monosaccharides.
    • Homo-polysaccharides: Composed of the same type of monosaccharides.
    • Hetero-polysaccharides: Composed of different types of monosaccharides.

Examples of Monosaccharides

  • Trioses: Glyceraldehyde, dihydroxyacetone
  • Tetroses: D-erythrose
  • Pentoses: D-ribose, D-glucose, D-fructose
  • Hexoses: D-glucose, D-fructose, D-galactose, D-mannose
  • Importance: Building blocks of other carbohydrates, structural components in nucleic acids, and primary energy source

Examples of Disaccharides

  • Sucrose: Glucose + Fructose
  • Lactose: Glucose + Galactose
  • Maltose: Glucose + Glucose
  • Isomaltose: Glucose + Glucose (different linkage than maltose)
  • Clinical Significance: Sucrose intolerance, lactose intolerance

Examples of Polysaccharides

  • Starch: Storage form of glucose in plants, important in food.
  • Glycogen: Storage form of glucose in animals, stored in liver and muscle.
  • Cellulose: Structural component of plant cell walls (important dietary fiber).
  • Chitin: Structural component of fungal cell walls and insect exoskeletons.
  • Dextran: Polysaccharide of glucose varying chain length.

Glycosidic Bonds

  • Bonds between monosaccharides.
  • Two types: O-glycosidic and N-glycosidic bonds
  • Formed when hydroxyl group on one monosaccharide reacts with the hydroxyl group of another.

Cellular Respiration

  • Glycolysis: Breakdown of glucose to pyruvate or lactate (cytosolic).
  • Citric Acid Cycle (TCA cycle): Further breakdown of pyruvate to Acetyl CoA.
  • Oxidative Phosphorylation: Generating most of the ATP in the mitochondria from reduced electron carriers.

Metabolic Fate of Pyruvate

  • Pyruvate can be transformed to Acetyl CoA, which is a major building block in the TCA cycle
  • Pyruvate can also be converted to lactate by lactate dehydrogenase, crucial for anaerobic conditions.
  • Pyruvate can also be converted to oxaloacetate by pyruvate carboxylase important for replenishing citric acid intermediates.

TCA Cycle

  • Acetyl CoA enters the TCA cycle.
  • Series of reactions leading to the oxidation of acetyl CoA to CO2.
  • Important for energy production.
  • Important intermediate for synthesis of fatty amino acids and other biomolecules.

Metabolism of Fructose

  • Fructose, a component of sucrose.
  • Metabolism occurs in the liver, intestinal mucosa, and kidneys.
  • Phosphorylation by fructokinase, the major mechanism.
  • Cleaved to glyceraldehyde-3-phosphate and dihydroxyacetone phosphate, which enter glycolysis.
  • Sorbitol pathway for fructose synthesis.

Metabolism of Galactose

  • Lactose hydrolysis produces glucose and galactose.
  • Galactose phosphorylated to galactose-1-phosphate, then to UDP-galactose.
  • UDP-galactose converted back to UDP-glucose, enters various pathways.
  • Galactose also used to synthesize other molecules.

Disorders

  • Defects in glycolytic enzymes can lead to various diseases and complications.
  • Common defects include those in hexokinase, phosphofructokinase, and pyruvate kinase.
  • There have also been described defects in the TCA cycle enzymes and pathways

Alcohol Metabolism

  • Alcohol converted to acetaldehyde by alcohol dehydrogenase
  • Acetaldehyde converted to acetate by aldehyde dehydrogenase
  • NADH levels increase, affecting the balance of pyruvate, lactate, and oxaloacetate -Alcohol's effects on metabolism can lead to hypoglycemia.

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Description

Explore the fascinating world of carbohydrates, their classifications, and examples. This quiz covers monosaccharides, oligosaccharides, and polysaccharides, including specific types like trioses and disaccharides. Test your knowledge on the chemical structures and classifications of these essential biomolecules.

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